Motor vehicles (e.g., motor cars) typically have a drive train having at least one internal combustion engine for producing driving power. The driving power is usually transmitted to drive wheels of the motor vehicle via a transmission (e.g., an automatic or manual transmission) and a final drive. The internal combustion engine of a motor vehicle is furthermore used to drive auxiliary units. For this purpose, an internal combustion engine usually has a belt drive, which is driven by a belt pulley coupled to a crankshaft of the internal combustion engine.
The belt drive may drive ancillary units of the motor vehicle (e.g., hydraulic pumps, water pumps, air-conditioning compressors and at least one electric generator). To enable a belt of the belt drive to transmit sufficient torque to the auxiliary units to be driven, tensioning devices for the belt may be used. Such tensioning devices usually operate with tensioning pulleys, which are placed against the belt, tensioning the belt with a spring preload, for example.
US 2009/0186726 A1 discloses a tensioning pulley arrangement for a belt drive of a mild-hybrid drive train, said arrangement having two tensioning pulleys, which are guided by means of pivotably mounted levers. At one end, the pivotably mounted levers are connected to a hydraulic piston of a hydraulic unit and, at the other end, they support the tensioning pulley. Additionally, U.S. Pat. No. 7,494,434 B2 discloses a mechanical tensioning pulley arrangement for a belt drive, wherein there is a rocker that can be pivoted relative to the internal combustion engine and which carries a tensioning pulley at one end. Arranged at the other end of the rocker is a pivotably mounted lever, at the free end of which a second tensioning pulley is arranged. The lever is spring-preloaded relative to the rocker. The rocker is likewise spring-preloaded in relation to the internal combustion engine. Tensioning pulley arrangements of this kind must have a high pretension, even in an idling state, in which relatively low forces have to be transmitted by the belt drive, to ensure that sufficiently high pre-tensioning forces are available in the dynamically loaded state to reliably prevent slippage and thus unwanted slip of the belt. However, at low loads the tensioning pulley system may have disadvantageous frictional losses within the belt drive due to excess belt tension. Therefore, previous tensioning systems, such as the systems disclosed US 2009/0186726 and U.S. Pat. No. 7,494,434 may have made disadvantageous trade-offs between dynamic load tensioning to reduce slippage and low load friction losses.
Recognizing the aforementioned problems the inventors developed a tensioning pulley arrangement. In one example, the tensioning pulley arrangement includes a first tensioning pulley and a second tensioning pulley tensioning a belt with a spring force and a spring preload force generated by a first spring device coupled to the first and second tensioning pulleys. The tensioning pulley arrangement further includes an intensifying device that decreases belt tension during low belt load conditions and increases belt tension during high belt load conditions. The intensifying device therefore enables belt slippage to be reduced during high peak loads and dynamic load swings and also reduces friction losses during low belt loads. In this way, the tensioning pulley arrangement may be efficiently operated over a wide range of operating conditions. In one example, the intensifying device may include a second spring device coupled to the first and second tensioning pulleys in parallel with the first spring device, the second spring device providing variable tensioning forces based on the distance between the first and second tensioning pulleys. Thus, when the second spring device is arranged in this manner the belt slippage and friction loss reductions can be achieved by a simple and low cost mechanism.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.